Guaranteed to be pseudorandom

Category Archives: Security

Summary
CompuLab have not enabled signature checking of firmware updates for the Intense PC product line. This allows anyone in possession of the Phoenix UEFI update program to write a modified UEFI firmware to system flash. DOS/Windows versions of the Phoenix utility are easily obtained online, allowing a local or remote attacker to install a persistent firmware level rootkit to the computer, or to corrupt the system firmware, causing a denial of service.

Installation of a modified firmware can occur entirely in the background, without any user interaction, and once performed is virtually impossible to difficult to detect using operating system utilities. Physical access is not required.

Product description
The CompuLab Intense PC is fanless mini-PC. A model pre-installed with Linux Mint is also marketed under the name MintBox 2. The system firmware is the same for the Intense PC and MintBox 2. CompuLab also sell the Intense PC with an extended temperature range for industrial applications.

The product was introduced in mid-2013 and is still being sold through Amazon US, Amazon Canada, Amazon Germany, Amazon Spain, and directly from CompuLab.

Affected products

Intense PC (Intense PC Value, Intense PC Business, Intense PC Pro)

MintBox 2

Impact
Any software running with local administrator privileges has unrestricted access to read and write the system’s firmware.

An attacker can modify the contents of the system firmware to install a persistent rootkit/bootkit, or to corrupt the firmware causing the computer to cease functioning.

The attack only requires local administrator privileges, and can be executed either by using an existing OS-level exploit to gain local administrator, or via tricking the user into running an executable (e.g. via an attachment in a phishing email).

Proof of Concept
The proof of concept provided for CVE-2017-8083 can be leveraged for this vulnerability as well. The proof of concept uses the Phoenix UEFI Winflash utility to write a modified firmware to flash. Please refer to the article about CVE-2017-8083 for a detailed description of the proof of concept.

The latest CompuLab firmware for the Intense PC (20170521) modified with the upstream EDKII shell can be downloaded here.

Mitigation
At this time there is no means for the end user to enable Capsule Signature verification or to prevent the Phoenix update utility from updating the system firmware.

Therefore Intense PC owners should consider the following options:

Ensure your operating system is up to date with the latest security patches. Do not run software from untrusted sources.

Do not connect your Intense PC to any networks with internet access (i.e. air-gap the computer).

Discontinue your use of the Intense PC and consider replacing the computer with one from a different manufacturer who implements signature validation for firmware updates.

Should CompuLab decide to improve the security of the Intense PC firmware by enabling Capsule Signature validation, then the above recommendations would no longer apply. However, in my communication with CompuLab regarding this issue no indication was given that they have any plans to enable Capsule Signature verification in a future update. Therefore, it seems very unlikely to me CompuLab will issue an update which enables Capsule Signature verification.

Disclosure timeline:6 June 2017: Issue reported to CompuLab6 June 2017: CompuLab confirms that “Default settings of this source tree [Phoenix SecureCore Tiano Enhanced Intel Ivy Bridge CPU Panther Point M] has disabled Capsule Signature option.”6 June 2017: Issue is reported to MITRE6 June 2017: Vulnerability is assigned CVE-2017-94577 June 2017: CompuLab are informed that the vulnerability has been assigned CVE-2017-9457 and details of the vulnerability will be published after 45 days

Summary
CompuLab Intense PC and MintBox 2 fail to properly write protect flash regions, allowing an attacker with local administrator privileges to write arbitrary code to the platform firmware. This could allow a remote attacker to install a persistent firmware level rootkit to the computer, or to erase the system firmware, causing a denial of service.

Installation of a modified firmware can occur entirely in the background, without any user interaction, and once performed is virtually impossible to difficult to detect using operating system utilities. Physical access is not required.

Product description
The CompuLab Intense PC is fanless mini-PC. A model pre-installed with Linux Mint is also marketed under the name MintBox 2. The system firmware is the same for the Intense PC and MintBox 2. CompuLab also sell the Intense PC with an extended temperature range for industrial applications.

The product was introduced in mid-2013 and is still being sold through Amazon US, Amazon Canada, Amazon Germany, Amazon Spain, and directly from CompuLab.

Affected products

Intense PC (Intense PC Value, Intense PC Business, Intense PC Pro)

MintBox 2

At the time of discovery in March 2017, the latest firmware for CompuLab was dated 21 June 2016, and did not enable write protection on any flash regions.

Impact
Any software running with local administrator privileges has unrestricted access to read and write the system’s firmware.

An attacker can modify the contents of the system firmware to install a persistent rootkit/bootkit, or to corrupt the firmware causing the computer to cease functioning.

The attack only requires local administrator privileges, and can be executed either by using an existing OS-level exploit to gain local administrator, or via tricking the user into running an executable (e.g. via an attachment in a phishing email).

Proof of Concept
The firmware update from CompuLab was downloaded, decompressed, and loaded into UEFITool.

The default UEFI shell provided in Phoenix SecureCore was replaced with a newer version of the UEFI shell from EDK2:

The Phoenix SecureCore UEFI Shell was replaced with the EDK2 UEFI Shell.

The modified update was then written to the system firmware using the Phoenix UEFI Winflash utility:

Phoenix UEFI Winflash

It was later realized that the Phoenix UEFI Winflash utility includes a flag enabling a silent firmware update from the command line:

Phoenix UEFI Winflash supports silently updating the firmware from the command line

Using the /remote2 option removes all visual notifications that a firmware update is in progress. Additionally, when used with /console or /remote2 options, the Winflash utility does not reboot the platform when finished. The system continues to function normally, and there is no indication to the user that a firmware update has taken place at all.

WARNING: *******************************************************************
WARNING: Chipsec should only be used on test systems!
WARNING: It should not be installed/deployed on production end-user systems.
WARNING: See WARNING.txt
WARNING: *******************************************************************

Through my discussion with CompuLab support, it has emerged that the issue is due to CompuLab not running CloseMnf prior to shipping. CloseMnf stands for “Close of Manufacturing” and hardens the system by setting write-protect flags for the various flash regions in the Master Access Section of the Descriptor Region.

Intel documentation regarding CloseMnf:

Disclosure timeline:1 March 2017: Vulnerability is reported to CompuLab via their support email address2 March 2017: CompuLab replies they will create a beta BIOS to address the vulnerability6 March 2017: I request a timeline to fix the issue7 March 2017: CompuLab replies they will create a beta BIOS for testing and they “will provide an official public release in the future”8 March 2017: CompuLab replies with instructions to run closemnf via the Intel FPT tool8 March 2017: I inform CompuLab I am waiting for the official BIOS update to resolve the issue8 March 2017: CompuLab replies with copy of Intel FPT tool and requests “not to publish or disclose this information”8 March 2017: CompuLab is informed that details of the vulnerability will be published on 4 June 201723 April 2017: Issue is reported to MITRE24 April 2017: Vulnerability is assigned CVE-2017-80833 May 2017: CompuLab communicates that they will delay fixing this vulnerability until Intel provides an updated ME firmware to address CVE-2017-56894 May 2017: I inform CompuLab that details of this vulnerability will be published on 4 June 2017 as previously discussed11 May 2017: CompuLab sends a proposed fix for testing, the update script fails due to invalid command syntax for flashrom14 May 2017: I inform CompuLab of the invalid syntax and provide the correct usage, and confirm that the fix enables write-protection on the ME/BIOS/GbE regions of flash15 May 2017: CompuLab replies with a revised update script15 May 2017: I inform CompuLab that the syntax of the revised script is correct, however my unit has already been updated so I cannot re-test4 June 2017: Details of the vulnerability are published.

Secure Boot is a bit like SELinux: people who use it really like it, and tell all their friends to use it. For everyone else, apart from those who don’t know about or even notice Secure Boot, it’s an annoyance that they almost immediately disable.

We’ve looked at the Intel DK200 from a hardware perspective before. Now it’s time to look at it from a software perspective. “Internet of Things Gateway” is pretty generic, so what can it actually do?

Following the instructions, I tried to register the system on Intel’s website so I could download the Wind River Intelligent Device Platform XT 2.0 SDK. I didn’t get very far:

Stormtrooper #1: This is not the product you’re looking for

Yeah… I guess this is what Mouser meant when they said the DK200 was End of Life.

Since this ships with the Linux Kernel, which is GPLv2 licensed, I believe Intel may be violating the GPL. Specifically:

Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange

But I am not a lawyer, and I am not really that interested in starting a legal battle over the source code for an ancient version of Wind River Linux I am not interested in using anyway.

So let’s go try to build Yocto. The Intel rep did say there was a Yocto BSP coming “soon” but “soon” in Intel time seems kind of variable.

After some hiccups (Yocto needs python2 and GCC <6) I had built a Yocto image and put it on an SD card. Does it boot?

…no

So we can’t boot Yocto because this is a “secure SKU” which means Secure Boot is enabled. Is there some way we can disable Secure Boot? What about updating the BSP to a newer version with Secure Boot disabled?

Back to hardware
If I’ve learned anything from messing around with electronics, you want to make a backup before you start modifying things. This is doubly so if the data in question is related to the booting process. It sucks to end up with a brick, so make a backup!

Taking a backup of flash

The Intel Quark guide mentions using a Dediprog SF100 to flash EDKII. I don’t have a Dediprog, but I do have an SPI programmer. Unfortunately, none of the Intel documentation I could find mentions the Dediprog header on the DK200, so I had to go hunting.

I traced the pins from the Winbond flash to header J23. J23 is only 8 pins, so trial and error with a multimeter to find the pin mapping wasn’t terrible:

J23 pinout

Here’s the pinout of J23 in text form:

J23 pin

25Q64 pin

Pin description

1

8

VCC

2

4

GND

3

1

/CS

4

6

CLK

5

2

DO

6

5

DI

7

Not connected

8

Not connected

/WP and HOLD pins on the 25Q64FV are not routed to J23, but they aren’t required for flashing.

With the pinout known, I could attach the SPI programmer to the header instead of using the chip clip:

J23 to ch341a SPI programmer

I took a dump of the Winbond 25Q64FV and then for good measure desoldered the chip and read it again to confirm the images were exactly the same. It was strange because the image from the chip clip wasn’t identical. But, the image from the desoldered chip was identical to the image taken from J23, so we’re done here. I wrote the image to a new 25Q64FV and soldered that back onto the board.

I assume that had I been able to download the WindRiver SDK, I would have been able to build and sign Secure Boot with my own certificates. Given that industrial customers spend a lot of time and money worrying about security, I was surprised to see that the Secure Boot certificate in the firmware was created by WindRiver China.

I did try to load up the image in IDA, but not being a power user of IDA, I couldn’t figure out how to get it to analyze the SPI dump, and gave up to try and compile the firmware from source.

Building the BSP

Being Intel, there are hundreds of pages you can read about developing for EDK2 and other really fun things, probably. I didn’t read them.

A document which I did end up reading religiously was the Intel ® QuarkTM SoC X1000 Board Support Package (BSP) Build and Software User Guide[PDF] which describes how to build all the firmware components needed to bring up the X1000 SoC. I found out there is actually a newer version of this document (1.2.1 instead of 1.1) and there are some important differences between the documents I want to get to later.

By building the firmware, we’re hoping for one of two outcomes:

A firmware with our own Secure Boot certificates, or

A firmware which has Secure Boot disabled

Version 1.1 of the BSP Build and Software User Guide includes a section on pages 29 and 30 on how to bundle your own db, kek, and pk certificates:

Page 29 and 30 condensed

Unfortunately if you follow the instructions and try to use a layout.conf which specifies these files, you’ll get an error because there’s no address specified for this data in the image:

I do have a reference file from WindRiver with Secure Boot certificates, so if I was really interested in making Secure Boot work as intended, I could have reverse engineered the address to store the certificates.

The certificates section of layout.conf was removed from the 1.2.1 revision of the BSP Build and Software User Guide. I guess since it no longer works, Intel decided to remove it from the documentation.

So, we can’t install our own Secure Boot certificates in the firmware. What happens if we just leave out the certificates section entirely and build it?

Error 37: Quark signature file not found

Right, so even though there’s now no certificate in the firmware bundle, we still can’t boot.

Interestingly, if you don’t partition the uSD or USB stick correctly, you end up with this pretty screen:

I never saw that in the stock firmware.

Hacking GRUB
So it seems that we can’t include our own Secure Boot certificate in the firmware, due to the sample layout.conf file missing the certificates section, and not knowing the appropriate address to store the certificates.

What if we dig into Error 37: Quark signature file not found a bit more?

If you look in the grub source code included in the BSP, you can see a giant ~1000KB patch that Intel has made to the original upstream code to support the Quark platform.

Going back to Intel’s modifications to grub, we can see what they added:

It takes a bit of searching, but if you strip out all of the grub_quark_secure logic from linux.c and boot_settings.c, you end up with…

Ta-da! I can boot Yocto Linux

No more Secure Boot!

At the end of the day, the Quark X1000 is an x86: “secure SKU” is nothing but a fuse setting.

The comment should read:

Determine whether or not grub should enforce Secure Boot.

In our case, this is not a mandatory option 😉

Special offer for DK200 owners
As shown above, it is possible to modify the Intel sources to disable Secure Boot. If there are other people have a DK200 from Intel and are interested in running a firmware without Secure Boot, leave a comment with your contact details. Upon request, I can provide a firmware image* with generic Ethernet MAC addresses for you to flash. Note that this firmware is specific to the DK200 (Clanton Hill) hardware.

* No warranty, express or implied, provided for said firmware image. You flash at your own risk!